In late August 1938, US secretary of state Cordell Hull flew to Berlin to warn the Nazi regime against attacking its neighbours. The superpower’s foreign policy chief stopped off in Prague to show support for Czechoslovakia. He also went to Paris and London, to tell the French and the British not to do deals with Hitler. Meanwhile the US ambassador to Moscow, Joseph Davies, delivered a blunt message to Stalin. None of that happened. In fact, the US was militarily feeble and absent from European security. Britain and France appeased Hitler. Poland and Lithuania were at loggerheads. Estonia and Latvia...